[cxx]: simple spi master class

* spi cxx unit test (CATCH-based, on host)
* added portmacro.h to driver mocking
* added simple testing app to write/read SPI,
  using an MPU9250

examples/cxx/experimental/simple_spi_rw_example/CMakeLists.txt

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+# The following lines of boilerplate have to be in your project's CMakeLists
+# in this exact order for cmake to work correctly
+cmake_minimum_required(VERSION 3.5)
+
+set(EXTRA_COMPONENT_DIRS "$ENV{IDF_PATH}/examples/cxx/experimental/experimental_cpp_component")
+
+include($ENV{IDF_PATH}/tools/cmake/project.cmake)
+project(simple_spi_rw_example)

examples/cxx/experimental/simple_spi_rw_example/README.md

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+# Example: C++ SPI sensor read for MCU9250 inertial/giroscope sensor
+
+(See the README.md file in the upper level 'examples' directory for more information about examples.)
+
+This example demonstrates usage of C++ SPI classes in ESP-IDF to read the `WHO_AM_I` register of the sensor.
+
+In this example, the `sdkconfig.defaults` file sets the `CONFIG_COMPILER_CXX_EXCEPTIONS` option. 
+This enables both compile time support (`-fexceptions` compiler flag) and run-time support for C++ exception handling.
+This is necessary for the C++ SPI API.
+
+## How to use example
+
+### Hardware Required
+
+An MCU9250 sensor and any commonly available ESP32 development board.
+
+### Configure the project
+
+```
+idf.py menuconfig
+```
+
+### Build and Flash
+
+```
+idf.py -p PORT flash monitor
+```
+
+(Replace PORT with the name of the serial port.)
+
+(To exit the serial monitor, type ``Ctrl-]``.)
+
+See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.
+
+## Example Output
+
+If the sensor is read correctly:
+
+```
+...
+I (0) cpu_start: Starting scheduler on APP CPU.
+Result of WHO_AM_I register: 0x71
+I (437) gpio: GPIO[23]| InputEn: 0| OutputEn: 0| OpenDrain: 0| Pullup: 1| Pulldown: 0| Intr:0
+I (447) gpio: GPIO[25]| InputEn: 0| OutputEn: 0| OpenDrain: 0| Pullup: 1| Pulldown: 0| Intr:0
+I (457) gpio: GPIO[26]| InputEn: 0| OutputEn: 0| OpenDrain: 0| Pullup: 1| Pulldown: 0| Intr:0
+I (467) gpio: GPIO[27]| InputEn: 0| OutputEn: 0| OpenDrain: 0| Pullup: 1| Pulldown: 0| Intr:0
+
+Done
+```
+
+If there's an error with the SPI peripheral:
+```
+...
+I (0) cpu_start: Starting scheduler on APP CPU.
+E (434) spi: spicommon_bus_initialize_io(429): mosi not valid
+Coulnd't read SPI!
+```
+
+If the SPI pins are not connected properly, the resulting read may just return 0, this error can not be detected:
+```
+...
+I (0) cpu_start: Starting scheduler on APP CPU.
+Result of WHO_AM_I register: 0x00
+I (437) gpio: GPIO[23]| InputEn: 0| OutputEn: 0| OpenDrain: 0| Pullup: 1| Pulldown: 0| Intr:0
+I (447) gpio: GPIO[25]| InputEn: 0| OutputEn: 0| OpenDrain: 0| Pullup: 1| Pulldown: 0| Intr:0
+I (457) gpio: GPIO[26]| InputEn: 0| OutputEn: 0| OpenDrain: 0| Pullup: 1| Pulldown: 0| Intr:0
+I (467) gpio: GPIO[27]| InputEn: 0| OutputEn: 0| OpenDrain: 0| Pullup: 1| Pulldown: 0| Intr:0
+```

examples/cxx/experimental/simple_spi_rw_example/main/CMakeLists.txt

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+idf_component_register(SRCS "simple_spi_rw_example.cpp"
+                    INCLUDE_DIRS "."
+                    REQUIRES experimental_cpp_component)

examples/cxx/experimental/simple_spi_rw_example/main/component.mk

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+#
+# "main" pseudo-component makefile.
+#
+# (Uses default behaviour of compiling all source files in directory, adding 'include' to include path.)

examples/cxx/experimental/simple_spi_rw_example/main/simple_spi_rw_example.cpp

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+/*
+ * SPDX-FileCopyrightText: 2021 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: CC0
+ *
+ * MPU9250 SPI Sensor C++ Example
+ *
+ * This example code is in the Public Domain (or CC0 licensed, at your option.)
+ *
+ * Unless required by applicable law or agreed to in writing, this
+ * software is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+ * CONDITIONS OF ANY KIND, either express or implied.
+*/
+
+#include <iostream>
+#include "spi_host_cxx.hpp"
+
+using namespace std;
+using namespace idf;
+
+static const GPIONum NSS(23);
+static const uint8_t READ_FLAG = 0x80;
+static const uint8_t MPU9250_WHO_AM_I_REG_ADDR = 0x75;
+
+extern "C" void app_main(void)
+{
+    try {
+
+        SPIMaster master(SPINum(2),
+                MOSI(25),
+                MISO(26),
+                SCLK(27));
+
+        shared_ptr<SPIDevice> spi_dev = master.create_dev(CS(NSS.get_num()), Frequency::MHz(1));
+
+        vector<uint8_t> write_data = {MPU9250_WHO_AM_I_REG_ADDR | READ_FLAG, 0x00};
+        vector<uint8_t> result = spi_dev->transfer(write_data).get();
+
+        cout << "Result of WHO_AM_I register: 0x";
+        printf("%02X", result[1]);
+        cout << endl;
+
+        this_thread::sleep_for(std::chrono::seconds(2));
+
+    } catch (const SPIException &e) {
+        cout << "Coulnd't read SPI!" << endl;
+    }
+}

examples/cxx/experimental/simple_spi_rw_example/sdkconfig.defaults

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+# Enable C++ exceptions and set emergency pool size for exception objects
+CONFIG_COMPILER_CXX_EXCEPTIONS=y
+CONFIG_COMPILER_CXX_EXCEPTIONS_EMG_POOL_SIZE=1024